A stirling engine has an advantage in that higher heat efficiency is expected. Moreover, the stirling engine, which is an external combustion engine, of which working fluid is heated externally, has another advantage in that it contributes to energy saving because it may exploit a wide variety of alternative energy of low temperature-gradient such as solar, geothermal, and exhaust heats, regardless of heat source.
Conventionally, the stirling engine as shown in FIG. 41 has been known. A high-temperature cylinder 102 and a low-temperature cylinder 103 are provided in the form of protrusions in an engine room 101. A heater 104 is connected to the upper side of the high-temperature cylinder 102 and a cooler 105 is connected to the low-temperature cylinder 103. The heater 104 and the cooler 105 are connected to one another via a regenerator 106. An expanding piston 107 and a compressing piston 108 are reciprocally disposed at the high-temperature cylinder 102 and the low-temperature cylinder 103, respectively. The pistons 107, 108 are connected to a crankshaft 111 by means of connecting rods 109, 110, respectively to reciprocate at a predetermined phase difference, for example, at an angle of 90° relative to one another.
A working fluid, for example, He, H2, or N2, is filled in the high-temperature cylinder 102, the low-temperature cylinder 103, the heater 104, the cooler 105, the regenerator 106, and a plumping system connecting them. An expansion space on the upper side of the high-temperature cylinder 102 and a compression space on the upper side of the low-temperature cylinder 103 are sealed by means of piston rings 112, 113 attached to the pistons 107, 108, respectively.
The working fluid, when being heated by a heat source (not shown) at the heater 104, expands and presses down the expanding piston 107, whereby the crankshaft rotates. On the other hand, when the expanding piston switches its movement to a rising stroke, the working fluid is carried into the regenerator 106 through the heater 104. At the regenerator 106, the working fluid transfers its heat to a filled thermal storage medium, flows out to the cooler 105 for cooling, and is compressed as the compressing piston 108 rises. The working fluid compressed in this way flows back into the heater 104 while drawing heat from the thermal storage medium in the regenerator 106 to produce an increase in its temperature, and flows into the heater 104, where it is heated by the heat source for expansion again.
Japanese Patent Application Laid-Open No. H4-311656 (Patent Document 1) discloses a stirling engine wherein a piston pin is guided by means of a Watt Z-shaped linear approximation link mechanism.
Further, a technique, by which a gas bearing is inserted between a piston and a cylinder, is disclosed in Japanese Patent Application Laid-Open No. 2002-89985 (Patent Document 2). In the Patent Document 2, a sterling engine is described, which has been designed so that a gas, which is supplied toward the piston through orifices formed on the gas bearing pad of a cylinder, provides the piston with buoyancy to ensure a non-contact state or a light load applied between the piston and the cylinder, producing no or a less frictional force.
Patent Document 1: Japanese Patent Application Laid-Open No. H04-311656
Patent Document 2: Japanese Patent Application Laid-Open No. 2002-89985
Patent Document 3: Japanese Patent Application Laid-Open No. H05-256367